In some wells, it is desirable to individually and selectively create multiple fractures having adequate conductivity, usually a significant distance apart along a wellbore, so that as much of the hydrocarbons in an oil and gas reservoir as possible can be drained/produced into the wellbore. When stimulating a reservoir from a wellbore, especially those that are highly deviated or horizontal, it is difficult to control the creation of multi-zone fractures along the wellbore without cementing a liner to the wellbore and mechanically isolating the zone being fractured from previously fractured zones or zones not yet fractured.
Traditional methods to create fractures at predetermined points along a highly deviated or horizontal wellbore vary depending on the nature of the completion within the lateral (or highly deviated) section of the wellbore. Only a small percentage of the horizontal completions during the past 15 or more years used a cemented liner type completion; most used some type of non-cemented liner or a bare openhole section. Furthermore, many wells with cemented liners in the lateral were also completed with a significant length of openhole section beyond the cemented liner section. The best known way to achieve desired hydraulic fracturing isolation/results is to cement a solid liner in the lateral section of the wellbore, perform a conventional explosive perforating step, and then perform fracturing stages along the wellbore using some technique for mechanically isolating the individual fractures. The second most successful method involves cementing a liner and significantly limiting the number of perforations, often using tightly grouped sets of perforations, with the number of total perforations intended to create a flow restriction giving a back-pressure of about 100 psi or more, due to fluid flow restriction based on the wellbore injection rate during stimulation, with some cases approaching 1000 psi flow resistance. This technology is generally referred to as “limited entry” perforating technology.
In one conventional method, after the first zone is perforated and fractured, a sand plug is installed in the wellbore at some point above the fracture, e.g., toward the heel. The sand plug restricts any meaningful flow to the first zone fracture and thereby limits the loss of fluid into the formation, while a second upper zone is perforated and fracture stimulated. One such sand plug method is described in SPE 50608. More specifically, SPE 50608 describes the use of coiled tubing to deploy explosive perforating guns to perforate the next treatment interval while maintaining well control and sand plug integrity. The coiled tubing and perforating guns were removed from the well and then the next fracturing stage was performed. Each fracturing stage was ended by developing a sand plug across the treatment perforations by increasing the sand concentration and simultaneously reducing pumping rates until a bridge was formed. The paper describes how increased sand plug integrity could be obtained by performing what is commonly known in the cementing services industry as a “hesitation squeeze” technique. A drawback of this technique, however, is that it requires multiple trips to carry out the various stimulation and isolation steps.
More recently, Halliburton Energy Services, Inc. has introduced and proven the technology for using hydrajet perforating, jetting while fracturing, and co-injection down the annulus. In one method, this process is generally referred to by Halliburton as the SURGIFRAC process or stimulation method and is described in U.S. Pat. No. 5,765,642, which is incorporated herein by reference. The SURGIFRAC process has been applied mostly to horizontal or highly deviated wellbores, where casing the hole is difficult and expensive. By using this hydrajetting technique, it is possible to generate one or more independent, single plane hydraulic fractures; and therefore, highly deviated or horizontal wells can be often completed without having to case the wellbore. Furthermore, even when highly deviated or horizontal wells are cased, hydrajetting the perforations and fractures in such wells generally result in a more effective fracturing method than using traditional explosive charge perforation and fracturing techniques. Thus, prior to the SURGIFRAC technique, methods available were usually too costly to be an economic alternative, or generally ineffective in achieving stimulation results, or both.